1. Field of the Invention
This invention relates to reclamation processing of vinyl chloride polymer-containing materials and, more particularly, to methods of and apparatus for separating and recovering a recompoundable vinyl chloride polymer, particularly polyvinyl chloride (hereinafter PVC), from a polymeric scrap material, and to a recompoundable PVC resulting therefrom.
2. Description of the Prior Art
Scrap material including metal components generated during many industrial processes has for years been reprocessed to recover the metal therefrom. Copper, for example, has been recovered from telephone cables which have been scrapped at some stage of the manufacturing process. Telephone cables which have been removed from service have likewise been reprocessed. The residue from prior art metal reclaiming processes has included middlings of textile, plasticizers, pigments and fillers as well as a basic insulating plastic compound such as PVC. Only limited use has been found for this residue, as such, and to date the residue has not been convertible economically into its individual components.
The residue has been disposed of by incineration or used as land fill. Ecological considerations now require more desirable disposal procedures. Moreover, economic factors similar to the high cost and uncertain supply of copper which have historically justified copper reclaiming, have come to apply to polymers and plasticizers under present international market conditions.
Recent industry efforts have been made, for example, to reclaim PVC for re-use. In general, it is well known that solvent recovery techniques can be employed for dissolving both PVC and associated plasticizers, which together are the major weight fraction of the nonmetallic components of scrap telephone cable. In this approach, the metal is readily separated, and the nonmetallic components can thereafter be recovered.
The published prior art (See, for example U.S. Pat. No. 3,836,486.) includes treating a scrap charge, which includes a plasticized PVC composition with a solvent, such as, for example, tetrahydrofuran, cyclohexanone or methylethyl ketone, to form a solvent mixture. The solvent mixture is then treated with a nonsolvent for PVC to precipitate out and separate a PVC composition from plasticizers, solvent and nonsolvent which are recovered subsequently for reuse.
The products recovered from the above-described process will vary in composition depending on the quantity of other soluble or suspendable particulate matter, such as plasticizers, flame retardants, fillers, and pigments, which were present in the original scrap charge. Where scrap material from a variety of sources is used, variations in the components of the scrap material are not readily controllable at the process input.
The PVC composition recovered by the above-mentioned process undesirably includes components, such as pigments and fillers, which would cause the recovered PVC to be unsuitable for use in insulating wires and cables where color coding is a consideration. In order to recover a PVC which is readily reusable in the wire and cable industry, a recovery process must include the capability of separating pigments and fillers, and other additives as well as the plasticizers, from the scrap material so that an essentially pure PVC resin is obtained.
In U.S. Pat. No. 3,043,785 a pigmented polymeric composition is advantageously depigmented by a process which includes dissolving the pigmented polymeric composition in a suitable nonreactive water insoluble organic solvent. A water-soluble cellulose ether is incorporated in an aqueous phase which is then mixed with the resulting organic solution containing a dispersed pigment to accelerate pigment settling, the cellulose ether facilitating flocculation of the pigment. Then the organic polymer solution is separated from the pigment and the aqueous phase advantageously by settling the organic polymer solution from the aqueous phase, separating the organic polymeric solution from the aqueous phase, filtering the separated polymeric solution, and subsequently isolating and recovering the reclaimed and depigmented polymer. See also U.S. Pat. No. 2,915,482.
The prior art also shows a polyethylene carbon black mixture dissolved in an organic solvent and the addition of a strongly acidic coagulant such as hydrochloric acid after which the mixture is refluxed. See U.S. Pat. No. 3,232,891.